THE construction project of the decade

This is the evocative title that La Gazette de Monaco chose in March 2017 for the first of a long series of articles relating to Monaco's offshore extension project. With each passing day, local residents better understand this ambitious project. Two years and several million tons of transported material later, the teams of the various contractors working on the site have achieved something they can be proud of. 

The schedule has been kept. Fears about certain operations have been dispelled. Environmental data is under control. The offshore extension project provides daily challenges, but the first two years of work have demonstrated the ability of the numerous stakeholders to keep their promises on a totally unique project with many highly specific constraints. 

"The future offshore extension, which will be home to a residential neighborhood, including some 60,000 square metres for housing units, is probably THE development project of the decade for Monaco. It will produce numerous opportunities, namely economic ones (new housing surfaces, related transfer rights...), but also complex technical challenges," as we mentioned in our issue 510. 

Having relocated the posidonia and noble pen shells, which was a very delicate and completely experimental endeavour, the rock had to be laid bare during a two-phase sediment removal operation. The top layer, made of "non-submerged" sediments, or "polluted" sediments as they are more commonly called, required a special treatment, which was carried out in a centre at Envisan, in the Var department. The lower layer was dispersed off the Monaco coastline. 

18 boxes in l8 months

It was then necessary to bring some 1,480,000 tons of quarry material from the Bouches-du-Rhône with a special boat to form the basement layer for future concrete foundations. These foundation boxes, of which there are 18, are as big as nine-storey buildings and each weighs around 10,000 tons. These were built in the Great Maritime Port of Marseille at the same time as the backfill preparation. 

A specific tool had to be constructed beforehand. The floating dock, which is a sort of offshore factory used to build concrete walls, was constructed in Poland and brought to Marseille by sea. For 18 months, local teams worked around the clock to pour the concrete. 

For Christophe Hirsinger, head of Bouygues TP Monaco, “this was a tremendous source of satisfaction. This very special operation was conducted with the greatest care". 

In the initial schedule, a slight delay had been foreseen for this operation. There was no such delay. 


In Monaco, although the first phases were conducted without a glitch, one item was revealed to be more complex than initially thought: the rock excavation under the foundations of the Fairmont hotel caused disruptions that went beyond the initial scope of work, forcing the Bouygues teams to quickly rethink their strategy and come up with new techniques. 

Last winter's weather conditions further hindered operations. The strong wind and swelling seas that marked the season caused much damage to the outcrops under construction, to the vibro-compaction needles, and even to the "gabiole", the small prefabricated unit used by the coordination teams and that overlooks the sea and construction site. Several operations to install the boxes had to be delayed because of poor weather conditions, but all 18 boxes should be in place by the end of next month, exactly according to the initial schedule. This operation has to comply with many conditions and constraints: the tolerance margin is of less than l0cm per element, which is truly challenging!

Schedule moved forward 

On two occasions, unforeseen requirements forced stakeholders to find new solutions to anticipate several subsequent operations. So, by the end of June 2019, "we completed the work nearly one year ahead of schedule!" the director of Bouygues TP Monaco is pleased to report concerning the terracing that will support the building designed by architect Renzo Piano. 


This article was originally published in the July-September 2019 edition of the Gazette de Monaco.